A photovoltaic cell or a solar cell is a cell capable of converting light energy into electric energy by using a photoelectric transformation element that is capable of generating photovoltaic power, when exposed to light. When the photovoltaic cell is exposed to light, it generates a voltage through terminals thereof and induces a flow of electrons. The magnitude of the electron flow is proportional to the collision strength of light on a photovoltaic cell junction formed on a cell surface.
Kinds of photovoltaic cells include a silicon wafer photovoltaic cell and a thin film photovoltaic cell. The silicon wafer photovoltaic cell includes a photoelectric transformation element prepared using a single crystal or polycrystalline silicon ingot, and a photoelectric transformation element used in the thin film photovoltaic cell is deposited on a substrate or a ferroelectric using a method such as sputtering or deposition.
Since the photovoltaic cell is brittle, it requires a support element for supporting the cells. The support element may be a light-transmissive front substrate arranged over a photoelectric transformation element. Also, the support element may be a back sheet arranged at the rear of the photoelectric transformation element. The photovoltaic cell may include both the light-transmissive front substrate and the back sheet. Generally, the front substrate or the back sheet may be made of rigid materials such as glass, flexible materials such as a metal film or sheet, or polymer plastic materials such as polyimides.
Generally, the back sheet is in the form of a rigid back skin to protect the rear surface of the photovoltaic cell. Various materials which may be applied to such a back sheet are known, and, for example, include a ferroelectric such as glass, an organic fluoropolymer such as ethylene tetrafluoroethylene (ETFE) or a polyester such as poly (ethylene terephthalate) (PET). Such materials may be applied alone or applied after being coated with a material such as SiOx.
The photovoltaic cell includes a photoelectric transformation element or photoelectric transformation elements that are electrically connected to each other, i.e. a photoelectric transformation element array. The photoelectric transformation element or the photoelectric transformation element array is encapsulated by an encapsulant. The encapsulant is used for encapsulation of the elements to protect them from external environments and used to form an integral module.
A conventionally used encapsulant is ethylene vinyl acetate (EVA). However, the EVA has low adhesive strength to other parts of the module. Therefore, if the EVA is used for a long period of time, delamination is readily induced, as well as lowered efficiency or corrosion due to moisture permeation is induced. Also, the EVA becomes discolored due to its low UV resistance and degrades the efficiency of the modules. Furthermore, the EVA has a problem of causing damage to the elements due to internal stress generated during curing processes.